把字符串转换成整数

public class Solution {
    public int StrToInt(String str) {
        char[] ch = str.toCharArray();
        int s = 1;
        long sum = 0;
        if(ch.length == 0)return 0;
        if(ch[0] == ‘-‘) s = -1;
        for(int i = (ch[0]==‘+‘ || ch[0]==‘-‘)?1:0; i < ch.length; i++) {
            if(ch[i]>=‘0‘ && ch[i]<=‘9‘){
                sum = sum * 10 + ch[i]-‘0‘;
            }else{
                return 0;
            }
        }
        sum = sum * s;
        return (int)sum;
    }
}